This invention relates to apparatus for measuring torque. More particularly, it involves apparatus for sensing the amount of previously applied torque to a fastener.
In a variety of manufacturing applications, it is imperative that the correct amount of torque be applied to a fastener. For example, in automotive applications, it is necessary to make sure that bolts have been tightened within a certain prescribed range of torque in order to properly fasten two parts together. It has been common procedure for a member of the quality control department to use a hand torque wrench to approximate the prior torque level by viewing the movement of the torque indicator just prior to the "give" or breakaway of the fastener. Later improvements of such a test included the use of a wrench which would maintain the position of the indicator at the maximum torque experienced.
Unfortunately, these prior art methods of sensing the applied torque were not very precise and not capable of being accurately reproduced from operator to operator. Even under ideal conditions the torque sensed was the "breakaway" torque which caused further relative movement of the fastener and not the torque delivered to the fastener in the first instance. Under true operating conditions even this breakaway torque could not be accurately sensed because the operator was not capable of instantaneously stopping the level of applied torque as soon as he noticed the fastener motion.